Semiconductor device and manufacturing method

ABSTRACT

Provided is a semiconductor device comprising a semiconductor substrate containing oxygen. An oxygen concentration distribution in a depth direction of the semiconductor substrate has a high oxygen concentration part where an oxygen concentration is higher on a further upper surface-side than a center in the depth direction of the semiconductor substrate than in a lower surface of the semiconductor substrate. The high oxygen concentration part may have a concentration peak in the oxygen concentration distribution. A crystal defect density distribution in the depth direction of the semiconductor substrate has an upper surface-side density peak on the upper surface-side of the semiconductor substrate, and the upper surface-side density peak may be arranged within a depth range in which the oxygen concentration is equal to or greater than 50% of a peak value of the concentration peak.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.17/209,242 filed on Mar. 23, 2021, which is a continuation ofInternational Patent Application PCT/JP2020/006920 filed on Feb. 20,2020; which claims priority to Japanese Patent Application No.2019-086038 filed on Apr. 26, 2019, the entirety of the contents of eachof which are hereby incorporated herein by reference.

BACKGROUND 1. Technical Field

The present invention relates to a semiconductor device and amanufacturing method.

2. Related Art

In the related art, known is a semiconductor device in which asemiconductor substrate is formed with semiconductor elements such as atransistor, a diode and the like (for example, refer to Patent Documents1 to 4).

CITATION LIST [Patent Document] Patent Document 1: Japanese PatentApplication Publication No. 2010-165772 Patent Document 2: JapanesePatent Application Publication No. 2012-238904 Patent Document 3:Japanese Patent Application Publication No. 2018-137454 Patent Document4: Japanese Patent Application Publication No. 2015-198166 TechnicalProblem

Characteristics of the semiconductor device may vary depending on aconcentration of oxygen included in the semiconductor substrate.

GENERAL DISCLOSURE

In order to solve the above problem, a first aspect of the presentinvention provides a semiconductor device comprising a semiconductorsubstrate containing oxygen. An oxygen concentration distribution in adepth direction of the semiconductor substrate may have a high oxygenconcentration part where an oxygen concentration is higher on a furtherupper surface-side than a center in the depth direction of thesemiconductor substrate than in a lower surface of the semiconductorsubstrate.

The high oxygen concentration part may have a concentration peak in theoxygen concentration distribution.

The oxygen concentration may decrease from the concentration peak towardthe lower surface of the semiconductor substrate until it becomes thesame as the oxygen concentration in the lower surface of thesemiconductor substrate.

A crystal defect density distribution in the depth direction of thesemiconductor substrate may have an upper surface-side density peak onthe upper surface-side of the semiconductor substrate. The uppersurface-side density peak may be arranged within a depth range in whichthe oxygen concentration is equal to or greater than 50% of a peak valueof the concentration peak. The upper surface-side density peak may alsobe arranged within a depth range in which the oxygen concentration isequal to or greater than 80% of the peak value of the concentrationpeak.

In the oxygen concentration distribution, the depth range in which theoxygen concentration is equal to or greater than 50% of the peak valueof the concentration peak may be equal to or greater than 10 μm.

The concentration peak may be arranged between the upper surface-sidedensity peak and the upper surface of the semiconductor substrate.

The peak value of the concentration peak may be 1.5 times or greater aslarge as a minimum value of the oxygen concentration in the oxygenconcentration distribution. The peak value of the concentration peak maybe 5 times or greater as large as the minimum value of the oxygenconcentration in the oxygen concentration distribution.

A distance between the concentration peak of the oxygen concentrationdistribution and the upper surface of the semiconductor substrate may beequal to or greater than 5 μm and equal to or smaller than 20 μm.

The semiconductor device may comprise a gate conductive portion providedin the upper surface of the semiconductor substrate and a gateinsulating film for insulating the gate conductive portion and thesemiconductor substrate from each other.

The semiconductor device may comprise a cathode region of a firstconductivity-type provided in contact with the lower surface of thesemiconductor substrate, and an anode region of a secondconductivity-type provided in contact with the upper surface of thesemiconductor substrate.

A second aspect of the present invention provides a manufacturing methodof a semiconductor device comprising a semiconductor substratecontaining oxygen. The manufacturing method may comprise an annealingstep of annealing an initial substrate so that a solid solubility limitconcentration of oxygen with respect to the initial substrate is to behigher than a current oxygen concentration in the initial substrate. Themanufacturing method may comprise a thinning step of thinning theinitial substrate from a lower surface-side of the initial substrate toform a semiconductor substrate.

The manufacturing method may comprise a preparation step of preparing anMCZ substrate as the initial substrate. The manufacturing method maycomprise a preparation step of preparing an FZ substrate as the initialsubstrate.

The summary clause does not necessarily describe all necessary featuresof the embodiments of the present invention. The present invention mayalso be a sub-combination of the features described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view pictorially showing a semiconductordevice 100 in accordance with one embodiment of the present invention.

FIG. 2 shows an example of an oxygen concentration distribution in adepth direction of a semiconductor substrate 10.

FIG. 3 shows another example of the oxygen concentration distribution inthe depth direction of the semiconductor substrate 10.

FIG. 4 shows some processes of a manufacturing method of thesemiconductor device 100.

FIG. 5 is a top view showing an example of the semiconductor device 100in accordance with one embodiment of the present invention.

FIG. 6 is an enlarged view of a region A shown in FIG. 5 .

FIG. 7 shows an example of a cross-sectional view taken along a line b-bin FIG. 6 .

FIG. 8 shows another example of the cross-sectional view taken along theline b-b in FIG. 6 .

FIG. 9 shows an example of an oxygen concentration distribution and acrystal defect density distribution in a J-J cross-section in FIG. 8 .

FIG. 10 shows a relation between the oxygen concentration and a forwardvoltage Vf when a semiconductor substrate having an oxygen concentrationdistribution that is substantially uniform in a depth direction isformed with an upper surface-side lifetime control region 92 as shown inFIG. 8 .

FIG. 11 compares characteristics of the semiconductor devices 100manufactured using two semiconductor substrates 10 having differentinitial concentrations of oxygen.

FIG. 12 shows another example of the semiconductor device 100.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, the present invention will be described through embodimentsof the invention. However, the following embodiments do not limit theinvention defined in the claims. Also, all combinations of featuresdescribed in the embodiments are not necessarily essential to solutionsof the invention.

As used herein, one side in a direction parallel to a depth direction ofa semiconductor substrate is referred to as ‘upper’ and the other sideis referred to as ‘lower’. One surface of two principal surfaces of asubstrate, a layer or other member is referred to as ‘upper surface’,and the other surface is referred to as ‘lower surface’. The ‘upper’ and‘lower’ directions are not limited to a gravity direction or a directionwhen mounting a semiconductor device.

As used herein, the technical matters may be described using orthogonalcoordinate axes of X-axis, Y-axis and Z-axis, in some cases. Theorthogonal coordinate axes simply specify a relative position of aconstitutional element, not limiting a specific direction. For example,the Z-axis does not limit a height direction with respect to the ground.Note that, the +Z-axis direction and the −Z-axis direction are oppositeto each other. When the Z-axis direction is simply described withoutdenoting +/−, it means a direction parallel to the +Z-axis and the−Z-axis. As used herein, when seen from the +Z-axis direction, it mayalso be referred to “as seen from above”.

As used herein, the description “same” or “equal” may include a casewhere there is an error due to manufacturing variation and the like. Theerror is, for example, within 10%.

As used herein, a conductivity type of a doped region in whichimpurities are doped is described as P type or N type. The conductivitytypes of each of the doped regions may also be opposite polarities.Also, as used herein, P+ type or N+ type means that a dopingconcentration is higher than P type or N type, and P− type or N− typemeans that a doping concentration is lower than P type or N type. Also,as used herein, P++ type or N++ type means that a doping concentrationis higher than P+ type or N+ type.

As used herein, a doping concentration refers to a concentration ofimpurities activated as donors or acceptors. As used herein, aconcentration difference of donors and acceptors may also be defined asthe doping concentration. The concentration difference may be measuredby a voltage-capacitance measurement method (CV method). A carrierconcentration that is measured by a spreading resistance (SR)measurement method may also be defined as the doping concentration.Also, in a case where a doping concentration distribution has a peak,the peak value may be defined as the doping concentration in the region.In a case where the doping concentration in a region in which donors oracceptors are present is substantially uniform, for example, an averagevalue of the doping concentration may also be defined as the dopingconcentration in the region. As used herein, a concentration of dopantsindicates a concentration of each of donors and acceptors.

FIG. 1 is a cross-sectional view pictorially showing a semiconductordevice 100 in accordance with one embodiment of the present invention.The semiconductor device 100 comprises a semiconductor substrate 10. Thesemiconductor substrate 10 is a substrate formed of a semiconductormaterial such as silicon, compound semiconductor or the like. In thepresent example, the semiconductor substrate 10 is a silicon substrate.

The semiconductor substrate 10 has an upper surface 21 and a lowersurface 23. The upper surface 21 and the lower surface 23 are twoprincipal surfaces facing each other. In FIG. 1 , a direction connectingthe upper surface 21 and the lower surface 23 (i.e., a depth directionof the semiconductor substrate 10) is defined as a Z-axis direction.Also, two orthogonal axes parallel to the upper surface 21 and the lowersurface 23 are defined as an X-axis and a Y-axis. The semiconductorsubstrate 10 is formed with semiconductor elements such as a transistor,a diode and the like, which are omitted in FIG. 1 .

The semiconductor device 100 may comprise an upper surface-sideelectrode 141 and a lower surface-side electrode 142. The uppersurface-side electrode 141 is a metal electrode arranged above the uppersurface 21. The lower surface-side electrode 142 is a metal electrodearranged below the lower surface 23. The upper surface-side electrode141 and the lower surface-side electrode 142 may be provided in contactwith the semiconductor substrate 10, or an interlayer dielectric filmmay be provided between the upper surface-side electrode 141 and thesemiconductor substrate 10, and between the lower surface-side electrode142 and the semiconductor substrate 10. In FIG. 1 , the interlayerdielectric film is omitted.

The semiconductor substrate 10 contains oxygen. Oxygen may be containedin the entire semiconductor substrate 10. Characteristics of thesemiconductor device 100 vary depending on a concentration of oxygencontained in the semiconductor substrate 10.

For example, the semiconductor substrate 10 may be formed with a defectlevel for adjusting a lifetime of carrier. The defect level may beformed by irradiating the semiconductor substrate 10 with particles suchas helium ions or hydrogen ions (for example, protons), electron beamsor the like. When particles such as helium ions are irradiated, vacancy(V) is generated in the semiconductor substrate 10, and vacancy andoxygen combine to generate a VO defect. The carrier recombines with theVO defect and the like, so that the lifetime of carrier is reduced. Adensity of the VO defects depends on an oxygen concentration in thesemiconductor substrate 10. Therefore, even though helium ions or thelike are irradiated in similar conditions, when variation in oxygenconcentration occurs in the semiconductor substrate 10, thecharacteristics such as the lifetime of carrier vary.

The semiconductor substrate 10 is a chip individualized from a wafer cutfrom an ingot that is formed by a method such as an MCZ (Magneticfieldapplied Czochralski) method, an FZ (Floating Zone) method and the like.In the semiconductor substrate 10, oxygen introduced intentionally orunintentionally during a manufacturing process is contained. However,the oxygen concentration in the semiconductor substrate 10 varies due tovariations in manufacturing conditions and the like.

In the present example, for a substrate in a wafer or chip state,annealing is performed at a predetermined annealing temperature for apredetermined annealing time. During the annealing, a surface of thesubstrate is exposed to an oxygen containing atmosphere or is formedwith an oxide film. The annealing time is such a long time that oxygenhaving a concentration of a solid solubility limit corresponding to theannealing temperature is introduced into the substrate. The annealingtime may be 1 hour or longer, 2 hours or longer or 10 hours or longer.The solid solubility limit of oxygen indicates a limit concentration ofoxygen that can be dissolved in the substrate, and changes depending onthe annealing temperature.

The substrate is annealed for a predetermined annealing time or longer,so that oxygen having a concentration, which substantially coincideswith the solid solubility limit, is introduced in the vicinity of atleast a surface of the substrate. For this reason, it is possible tocontrol the oxygen concentration in the semiconductor substrate 10 bymanaging the annealing temperature so as to be the solid solubilitylimit corresponding to a desired oxygen concentration. In addition,since the annealing temperature can be managed relatively easily, it isalso possible to reduce variation in oxygen concentration amongsubstrates.

FIG. 2 shows an example of an oxygen concentration distribution in thedepth direction of the semiconductor substrate 10. In FIG. 2 , avertical axis is a logarithmic axis indicating the oxygen concentrationper a unit volume, and a horizontal axis is a linear axis indicating adepth position in the semiconductor substrate 10. FIG. 2 shows an oxygenconcentration distribution in a K-K cross-section in FIG. 1 . In FIG. 2, the oxygen concentration in the semiconductor substrate 10 before theannealing process is denoted as an initial concentration Ob. The initialconcentration Ob corresponds to an oxygen concentration in a substratein a wafer state.

The annealing process introduces oxygen into the semiconductor substrate10 from the upper surface 21. Note that, the annealing temperature is atemperature at which the solid solubility limit becomes greater than theinitial concentration Ob. Since oxygen diffuses from the upper surface21 toward an inside of the semiconductor substrate 10, the oxygenconcentration becomes smaller away from the upper surface 21.

Oxygen is also similarly introduced from the lower surface 23 of thesemiconductor substrate 10. In the semiconductor substrate 10 of thepresent example, however, a thickness of the semiconductor substrate 10is adjusted by grinding the semiconductor substrate 10 from the lowersurface 23-side after the annealing process. In the present example, thegrinding is performed over a range wider than a depth range within whichoxygen is introduced from the lower surface 23-side. For this reason, inthe oxygen concentration distribution shown in FIG. 2 , the oxygenconcentration becomes smaller toward the lower surface 23.

The oxygen concentration distribution in the semiconductor substrate 10has a high oxygen concentration part 143 where the oxygen concentrationis higher on the further upper surface 21-side than a center Dc in thedepth direction of the semiconductor substrate 10 than in the lowersurface 23 of the semiconductor substrate 10. In the example of FIG. 2 ,the oxygen concentration in the lower surface 23 of the semiconductorsubstrate 10 is denoted as O23. As described above, the annealingprocess is performed at the annealing temperature at which the solidsolubility limit becomes greater than the initial concentration Ob.Thereby, oxygen having a concentration corresponding to the solidsolubility limit is introduced within a predetermined distance from theupper surface 21 of the semiconductor substrate 10, and the oxygenconcentration is reduced away from the upper surface 21. For thisreason, the high oxygen concentration part 143 where the oxygenconcentration is higher than the lower surface 23 is formed on the uppersurface 21-side of the semiconductor substrate 10. By the aboveconfiguration, it is possible to accurately control the oxygenconcentration in the semiconductor substrate 10 by the annealingtemperature.

The high oxygen concentration part 143 may have a concentration peak 144in the oxygen concentration distribution. The concentration peak 144 isa point at which the oxygen concentration becomes largest in the oxygenconcentration distribution. In the present example, an oxygenconcentration at the concentration peak 144 is denoted as Omax. Theoxygen concentration Omax may coincide with the solid solubility limitthat is determined by the annealing temperature.

While the temperature of the semiconductor substrate 10 returns to roomtemperatures as the annealing process is over, oxygen in the vicinity ofthe upper surface 21 of the semiconductor substrate 10 may be releasedto an outside of the semiconductor substrate 10. Thereby, in thesemiconductor substrate 10 of the present example, the concentrationpeak 144 occurs in the oxygen concentration distribution. The oxygenconcentration distribution has an upper surface-side slope 146 betweenthe concentration peak 144 and the upper surface 21 and a lowersurface-side slope 145 between the concentration peak 144 and the lowersurface 23. Each slope is a region in which the oxygen concentrationbecomes smaller away from the concentration peak 144.

The oxygen concentration distribution in the depth direction of thesemiconductor substrate 10 may decrease from the concentration peak 144toward the lower surface 23 of the semiconductor substrate 10 until itbecomes the same as the oxygen concentration O23 in the lower surface 23of the semiconductor substrate 10. The oxygen concentration in the lowersurface-side slope 145 of the present example continuously decreasesfrom the concentration peak 144 to the lower surface 23. A gradient ofthe lower surface-side slope 145 may be gentler than a gradient of theupper surface-side slope 146. Thereby, it is possible to make a moderatechange in oxygen concentration over a wide region of the semiconductorsubstrate 10.

An oxygen concentration in the upper surface 21 of the semiconductorsubstrate 10 is denoted as O21. In the present example, the oxygenconcentration in the upper surface-side slope 146 continuously decreasesfrom the oxygen concentration Omax at the concentration peak 144 to theoxygen concentration O21 in the upper surface 21. The oxygenconcentration O21 may be higher than the initial concentration Ob. Theoxygen concentration O21 may also be lower or higher than the oxygenconcentration O23. The oxygen concentration O21 may also coincide with aminimum value Omin of the oxygen concentration in the semiconductorsubstrate 10.

A distance between the concentration peak 144 and the upper surface 21in the depth direction may be equal to or greater than 5 μm and equal toor smaller than 20 μm. A depth position of the concentration peak 144can be controlled by the annealing temperature and the annealing time.The depth position of the concentration peak 144 may be ¼ or less, ⅕ orless or 1/10 or less of the thickness of the semiconductor substrate 10in the depth direction. The concentration peak 144 may be provided overa predetermined depth range. That is, the oxygen concentrationdistribution may be provided with a region of the oxygen concentrationOmax over a predetermined depth range.

FIG. 3 shows another example of the oxygen concentration distribution inthe depth direction of the semiconductor substrate 10. Also in theoxygen concentration distribution of the present example, the oxygenconcentration decreases from the concentration peak 144 toward the lowersurface 23 of the semiconductor substrate 10 until it becomes the sameas the oxygen concentration O23 in the lower surface 23 of thesemiconductor substrate 10. However, the oxygen concentrationdistribution has a flat region 147 in which the oxygen concentrationcoincides with the oxygen concentration O23 over a predetermined depthrange from the lower surface 23. The flat region 147 may be arranged ina region on the lower surface 23-side of the semiconductor substrate 10(i.e., a region from the center position Dc to the lower surface 23) ormay be arranged extending up to a region on the upper surface 21-side(i.e., a region from the center position Dc to the upper surface 21).

Depending on the annealing conditions, there is a region inside thesubstrate in which oxygen from the upper surface 21 does not diffuse.The oxygen concentration in the region is substantially equal to theinitial concentration Ob. By grinding the lower surface 23-side so as toleave the region, it is possible to form the semiconductor substrate 10having the oxygen concentration distribution as shown in FIG. 3 .

In the examples of FIGS. 2 and 3 , the lower surface-side slope 145 maybe provided from a region on the upper surface 21-side to a region onthe lower surface 23-side. A length of the lower surface-side slope 145in the depth direction may be ⅕ or greater, ¼ or greater, ⅓ or greateror ½ or greater than the thickness of the semiconductor substrate 10 inthe depth direction. The length of the lower surface-side slope 145 inthe depth direction may also be 20 μm or longer, 30 μm or longer, 40 μmor longer or 50 μm or longer. The length of the lower surface-side slope145 in the depth direction may also be 2 times or greater, 4 times orgreater or 10 times or greater as large as a length of the uppersurface-side slope 146 in the depth direction.

FIG. 4 shows some processes of a manufacturing method of thesemiconductor device 100. In the manufacturing method of the presentexample, an initial substrate is prepared in a preparation step S400.The initial substrate may be an MCZ substrate formed by the MCZ method,an FZ substrate formed by the FZ method, or a substrate formed byanother method. As described above, the initial substrate is in a waferor chip state. An oxygen concentration in the initial substrate is theinitial concentration Ob.

Then, the initial substrate is annealed in an annealing step S401. Inthe annealing step S401, the initial substrate is annealed under oxygencontaining atmosphere or is annealed in a state where a natural oxidefilm is formed on a surface thereof. In the annealing step S401, theinitial substrate is annealed at a predetermined annealing temperaturefor a predetermined annealing time so that a solid solubility limitconcentration of oxygen with respect to the initial substrate is to behigher than a current oxygen concentration in the initial substrate. Thecurrent oxygen concentration refers to the initial concentration Obbefore the annealing process. After the annealing, the oxygenconcentration distribution on the upper surface-side of the initialsubstrate is similar to the distribution shown in FIG. 2 or FIG. 3 . Theoxygen concentration distribution on the lower surface-side of theinitial substrate is also similar to a distribution where the horizontalaxis of FIG. 2 or FIG. 3 is replaced with a depth position based on thelower surface.

The solid solubility limit of oxygen with respect to the siliconsubstrate is about 2×10¹⁷/cm³ when the annealing temperature is 1000°C., and about 5×10¹⁷/cm³ when the annealing temperature is 1150° C. Inthe annealing step S401, the annealing temperature at which the solidsolubility limit becomes greater than an initial oxygen concentration isset, according to the initial oxygen concentration in the initialsubstrate and a material of the initial substrate.

Subsequently, in an upper surface-side structure forming step S402, anupper surface-side structure of the semiconductor device 100 is formed.The upper surface-side structure includes an electrode and an insulatingfilm arranged above the upper surface 21 of the semiconductor substrate10, a doped region formed inside the semiconductor substrate 10, and thelike. The doped region refers to a region in which dopants areimplanted. For example, in a case where the semiconductor device 100 isa transistor, a structure on the upper surface 21-side includes anemitter electrode, an interlayer dielectric film, a gate conductiveportion, a gate insulating film, an emitter region of N type, a baseregion of P type, and the like. Note that, the annealing step S401 mayalso be performed during the upper surface-side structure forming stepS402. The annealing step S401 may also be performed before forming anemitter electrode on the upper surface of the initial substrate. Theannealing step S401 may also be a step common to or different fromanother annealing step for activating dopants, for example.

Subsequently, in a thinning step S403, the initial substrate is thinnedfrom the lower surface-side of the initial substrate to form thesemiconductor substrate 10. In the thinning step S403, the initialsubstrate may be thinned by CMP or the like. Thereby, the oxygenconcentration distribution in the semiconductor substrate 10 becomes thedistribution as shown in FIG. 2 or FIG. 3 .

Subsequently, in a lower surface-side structure forming step S404, alower surface-side structure of the semiconductor device 100 is formed.The lower surface-side structure includes an electrode arranged belowthe lower surface 23 of the semiconductor substrate 10, a doped regionformed inside the semiconductor substrate 10, and the like. For example,in a case where the semiconductor device 100 is a transistor, astructure on the lower surface 23-side includes a collector region of Ptype, and the like.

By the above processes, it is possible to manufacture the semiconductordevice 100 having the oxygen concentration distribution as shown in FIG.2 or FIG. 3 . Note that, the oxygen concentration on the upper surface21-side of the semiconductor substrate 10 can be controlled relativelyaccurately by the annealing temperature. On the other hand, since theinitial concentration Ob highly affects the oxygen concentration on thelower surface 23-side of the semiconductor substrate 10, variation inoxygen concentration is more likely to increase than the upper surface21-side. By forming a structure including a channel of a transistor andthe like on the upper surface 21-side of the semiconductor substrate 10,it is possible to further reduce variation in characteristics of thesemiconductor device 100.

The conditions in the annealing step S401 may be set so that aconcentration peak value Omax at the concentration peak 144 in theoxygen concentration distribution in the depth direction of thesemiconductor substrate 10 is 1.5 times or greater as large as theminimum value Omin of the oxygen concentration. The concentration peakvalue Omax is substantially equal to the solid solubility limitcorresponding to the annealing temperature. The minimum value Omin ofthe oxygen concentration is equal to or larger than the initialconcentration Ob. For this reason, by setting the concentration peakvalue Omax to 1.5 times or greater of the minimum value Omin, it ispossible to anneal the initial substrate at the solid solubility limitsufficiently higher than the initial concentration Ob. Thereby, it ispossible to reduce the variation in oxygen concentration in thesemiconductor substrate 10. Note that, when manufacturing a plurality ofsemiconductor devices 100, the annealing condition at which the solidsolubility limit is 1.5 times as large as the maximum initialconcentration Ob value of the initial concentrations Ob of the pluralityof initial substrates may be set. Each of the initial substrates issubjected to the annealing process at the set common annealingcondition. Thereby, it is possible to reduce variation in oxygenconcentration in each substrate by suppressing an influence of variationin the initial concentration Ob.

The concentration peak value Omax may be 5 times or greater or 10 timesor greater as large as the minimum value Omin. Thereby, it is possibleto further reduce the variation in oxygen concentration in thesemiconductor substrate 10.

FIG. 5 is a top view showing an example of the semiconductor device 100in accordance with one embodiment of the present invention. In FIG. 5 ,positions at which each of members is projected to the upper surface ofthe semiconductor substrate 10 are shown. In FIG. 5 , only some membersof the semiconductor device 100 are shown, and some members are omitted.

The semiconductor substrate 10 has end sides 102, as seen from above. Asused herein, “as seen from above” means seeing from the uppersurface-side of the semiconductor substrate 10. The semiconductorsubstrate 10 of the present example has two sets of ends 102 facing eachother, as seen from above. In FIG. 5 , the X-axis and the Y-axis areparallel to any one end side 102. The Z-axis is perpendicular to theupper surface of the semiconductor substrate 10.

The semiconductor substrate 10 is provided with an active portion 120.The active portion 120 is a region in which main current flows in thedepth direction between the upper surface and the lower surface of thesemiconductor substrate 10 when the semiconductor device 100 iscontrolled to an on-state. An emitter electrode is provided above theactive portion 120 but is omitted in FIG. 5 .

The active portion 120 is provided with transistor portions 70 eachincluding a transistor element such as an IGBT, and diode portions 80each including a diode element such as an FWD. In FIG. 5 , a region inwhich the transistor portion 70 is arranged is denoted with a referencesign “I”, and a region in which the diode portion 80 is arranged isdenoted with a reference sign “F”. The transistor portions 70 and thediode portions 80 are arranged side by side along a predeterminedarrangement direction (X-axis direction, in FIG. 5 ). The transistorportions 70 and the diode portions 80 may also be alternately arrangedside by side in the X-axis direction. As used herein, a directionperpendicular to the arrangement direction, as seen from above, may alsobe referred to as an extension direction (Y-axis direction, in FIG. 5 ).The transistor portions 70 and the diode portions 80 may each have along side in the extension direction. That is, a length of thetransistor portion 70 in the Y-axis direction is greater than a width inthe X-axis direction. Similarly, a length of the diode portion 80 in theY-axis direction is greater than a width in the X-axis direction. Thelongitudinal directions of the transistor portion 70 and the diodeportion 80 may be the same as or different from a longitudinal directionof a trench portion, which will be described later.

The diode portion 80 has a cathode region of N+ type in a region incontact with the lower surface of the semiconductor substrate 10. Asused herein, the region in which the cathode region is provided isreferred to as the diode portion 80. That is, the diode portion 80 is aregion overlapping the cathode region, as seen from above. The lowersurface of the semiconductor substrate 10 may also be provided with acollector region of P+ type, in a region other than the cathode region.As used herein, an extension region 81 in which the diode portion 80 isextended to a gate wire (which will be described later) in the Y-axisdirection may also be included in the diode portion 80. A lower surfaceof the extension region 81 is provided with a collector region.

The semiconductor device 100 may have one or more pads above thesemiconductor substrate 10. The semiconductor device 100 of the presentexample has a gate pad 112. The semiconductor device 100 may have ananode pad, a cathode pad and a current detection pad, in addition to thegate pad 112. Each pad is arranged in the vicinity of the end side 102.The vicinity of the end side 102 indicates a region between the end side102 and the emitter electrode, as seen from above. When mounting thesemiconductor device 100, each pad may be connected to an externalcircuit via a wire, for example.

The gate pad 112 is applied with a gate potential. The gate pad 112 iselectrically connected to a conductive portion of a gate trench portionof the active portion 120. The semiconductor device 100 has a gate wirefor connecting the gate pad 112 and the gate trench portion each other.In FIG. 5 , the gate wire is obliquely hatched.

The gate wire of the present example has an outer periphery gate wire130, and an active-side gate wire 131. The outer periphery gate wire 130is arranged between the active portion 120 and the end sides 102 of thesemiconductor substrate 10, as seen from above. The outer periphery gatewire 130 of the present example surrounds the active portion 120, asseen from above. As seen from above, a region surrounded by the outerperiphery gate wire 130 may also be set as the active portion 120. Theouter periphery gate wire 130 is also connected to the gate pad 112. Theouter periphery gate wire 130 is arranged above the semiconductorsubstrate 10. The outer periphery gate wire 130 may be a metal wireincluding aluminum and the like.

The active-side gate wire 131 is provided in the active portion 120. Theactive portion 120 is provided with the active-side gate wire 131, sothat it is possible to reduce variation in wire length from the gate pad112, for each region of the semiconductor substrate 10.

The active-side gate wire 131 is connected to a gate trench portion ofthe active portion 120. The active-side gate wire 131 is arranged abovethe semiconductor substrate 10. The active-side gate wire 131 may alsobe a wire formed of semiconductor such as polysilicon having impuritiesdoped therein.

The active-side gate wire 131 may also be connected to the outerperiphery gate wire 130. The active-side gate wire 131 of the presentexample is provided extending in the X-axis direction so as to traversethe active portion 120 from the outer periphery gate wire 130 on oneside to the outer periphery gate wire 130 on the other side at asubstantial center in the Y-axis direction.

The semiconductor device 100 may also comprise a temperature sensingunit (not shown) that is a PN-junction diode formed of polysilicon orthe like, and a current detection unit (not shown) for simulating anoperation of a transistor portion provided in the active portion 120.

The semiconductor device 100 of the present example comprises an edgetermination structure portion 90 between the outer periphery gate wire130 and the end side 102. The edge termination structure portion 90relaxes electric field concentration on the upper surface-side of thesemiconductor substrate 10. The edge termination structure portion 90has, for example, a guard ring provided in an annular shape withsurrounding the active portion 120, a field plate, RESURF and a combinedstructure thereof.

FIG. 6 is an enlarged view of a region A shown in FIG. 5 . The region Ais a region including the transistor portion 70, the diode portion 80and the active-side gate wire 131. In a region where the active portion120 and the outer periphery gate wire 130 are adjacent to each other,the outer periphery gate wire 130 may be arranged instead of theactive-side gate wire 131.

The semiconductor device 100 of the present example comprises gatetrench portions 40, dummy trench portions 30, a well region 11, emitterregions 12, base regions 14 and contact regions 15, which are providedinside the upper surface-side of the semiconductor substrate 10. Thegate trench portion 40 and the dummy trench portion 30 are each anexample of the trench portion. The semiconductor device 100 of thepresent example also comprises an emitter electrode 52 and anactive-side gate wire 131 provided above the upper surface of thesemiconductor substrate 10. The emitter electrode 52 and the active-sidegate wire 131 are provided separated from each other.

An interlayer dielectric film is provided between the emitter electrode52 and active-side gate wire 131 and the upper surface of thesemiconductor substrate 10 but is not shown in FIG. 6 . In theinterlayer dielectric film of the present example, contact holes 54 areprovided penetrating through the interlayer dielectric film. In FIG. 6 ,the contact holes 54 are each obliquely hatched.

The emitter electrode 52 is provided above the gate trench portions 40,the dummy trench portions 30, the well region 11, the emitter regions12, the base regions 14 and the contact regions 15. The emitterelectrode 52 is in contact with the emitter regions 12, the contactregions 15 and the base regions 14 in the upper surface of thesemiconductor substrate 10 via the contact holes 54. The emitterelectrode 52 is also connected to a dummy conductive portion in thedummy trench portion 30 via the contact holes provided in the interlayerdielectric film. The emitter electrode 52 may also be connected to thedummy conductive portion of the dummy trench portion 30 at an edge ofthe dummy trench portion 30 in the Y-axis direction.

The active-side gate wire 131 is connected to the gate trench portions40 through the contact holes provided in the interlayer dielectric film.The active-side gate wire 131 may also be connected to a gate conductiveportion of the gate trench portion 40 at an edge portion 41 of the gatetrench portion 40 in the Y-axis direction. The active-side gate wire 131is not connected to the dummy conductive portion in the dummy trenchportion 30.

The emitter electrode 52 is formed of a material including metal. InFIG. 6 , a range in which the emitter electrode 52 is provided is shown.For example, at least a part of a region of the emitter electrode 52 isformed of aluminum or an aluminum-silicon alloy. The emitter electrode52 may have a barrier metal formed of titanium, titanium compound, orthe like in a lower layer of the region formed of aluminum or the like.Also, the emitter electrode 52 may have a plug that is formed byembedding tungsten or the like so as to be in contact with the barriermetal and aluminum or the like, in the contact hole.

The well region 11 is provided overlapping the active-side gate wire131. The well region 11 is also provided to extend in a predeterminedwidth within a range that does not overlap the active-side gate wire131. The well region 11 of the present example is provided apart from anend of the contact hole 54 in the Y-axis direction toward theactive-side gate wire 131. The well region 11 is a secondconductivity-type region having a higher doping concentration than thebase region 14. In the present example, the base region 14 is P− type,and the well region 11 is P+ type.

Each of the transistor portion 70 and the diode portion 80 has aplurality of trench portions arranged in the arrangement direction. Inthe transistor portion 70 of the present example, one or more gatetrench portions 40 and one or more dummy trench portions 30 arealternately provided along the arrangement direction. In the diodeportion 80 of the present example, a plurality of dummy trench portions30 is provided along the arrangement direction. In the diode portion 80of the present example, the gate trench portion 40 is not provided.

The gate trench portion 40 of the present example may have two linearportions 39 (portions of the trench that are linear along an extensiondirection) extending along an extension direction perpendicular to thealignment direction and an edge portion 41 connecting the two extensionportions 39. The extension direction in FIG. 6 is the Y-axis direction.

At least a part of the edge portion 41 is preferably provided in acurved shape, as seen from above. The end portions of the two linearportions 39 in the Y-axis direction are connected each other by the edgeportion 41, so that electric field concentration at the end portions ofthe linear portions 39 can be relaxed.

In the transistor portion 70, the dummy trench portion 30 is providedbetween the respective linear portions 39 of the gate trench portion 40.One dummy trench portion 30 may be provided or a plurality of the dummytrench portions 30 may be provided between the respective linearportions 39. The dummy trench portion 30 may have a linear shapeextending in the extension direction, and may have linear portions 29and an edge portion 31, like the gate trench portion 40. Thesemiconductor device 100 shown in FIG. 6 comprises both the linear dummytrench portion 30 with no edge portion 31 and the dummy trench portion30 having the edge portion 31. Herein, each linear portion of eachtrench portion may be handled as one trench portion, in some cases.

A diffusion depth of the well region 11 may be greater than depths ofthe gate trench portion 40 and the dummy trench portion 30. The endportions of the gate trench portion 40 and the dummy trench portion 30in the Y-axis direction are provided in the well region 11, as seen fromabove. That is, a bottom of each trench portion in the depth directionat the end portion of each trench portion in the Y-axis direction iscovered with the well region 11. Thereby, the electric fieldconcentration on the bottom of each trench portion can be relaxed.

A mesa portion is provided between the respective trench portions in thearrangement direction. The mesa portion indicates a region sandwichedbetween the trench portions inside the semiconductor substrate 10. As anexample, an upper end of the mesa portion is the upper surface of thesemiconductor substrate 10. A depth position of a lower end of the mesaportion is the same as a depth position of a lower end of the trenchportion. The mesa portion of the present example provided extending theextension direction (Y-axis direction) along the trench in the uppersurface of the semiconductor substrate 10. In the present example, thetransistor portion 70 is provided with mesa portions 60, and the diodeportion 80 is provided with mesa portions 61. Herein, when simplyreferring to the mesa portion, it indicates each of the mesa portion 60and the mesa portion 61.

A mesa portion 60, which is in contact with the gate trench portion 40and is provided with the emitter region 12, of the mesa portions 60 isreferred to as a gate mesa portion. In the present example, the mesaportions 60 of the transistor portion 70 are all the gate mesa portions.In another example, the transistor portion 70 may have a dummy mesaportion that is not in contact with the gate trench portion 40 or is notprovided with the emitter region 12.

Each of the mesa portions is provided with the base region 14. A regionin each mesa portion, which is arranged the closest to the active-sidegate wire 131, of the base region 14 exposed on the upper surface of thesemiconductor substrate 10 is referred to as a base region 14-e. In FIG.6 , the base region 14-e arranged at one end portion of each mesaportion in the extension direction is shown. However, the base region14-e is also arranged at the other end portion of each mesa portion. Ineach mesa portion, at least one of the emitter region 12 of a firstconductivity-type and the contact region 15 of a secondconductivity-type may be provided in a region sandwiched between thebase regions 14-e, as seen from above. In the present example, theemitter region 12 is N+ type and the contact region 15 is P+ type. Theemitter region 12 and the contact region 15 may also be provided betweenthe base region 14 and the upper surface of the semiconductor substrate10 in the depth direction.

The mesa portion 60 of the transistor portion 70 has the emitter region12 exposed on the upper surface of the semiconductor substrate 10. Theemitter region 12 is provided in contact with the gate trench portion40. The mesa portion 60 in contact with the gate trench portion 40 mayalso be provided with the contact region 15 exposed on the upper surfaceof the semiconductor substrate 10.

In the mesa portion 60, each of the contact region 15 and the emitterregion 12 is provided from one trench portion to the other trenchportion in the X-axis direction. As an example, the contact region 15and the emitter region 12 of the mesa portion 60 are alternatelyarranged along the extension direction (Y-axis direction) of the trenchportion.

In another example, the contact region 15 and the emitter region 12 ofthe mesa portion 60 may be provided in a stripe shape along theextension direction (Y-axis direction) of the trench portion. Forexample, the emitter region 12 is provided in a region in contact withthe trench portion, and the contact region 15 is provided in a regionsandwiched between the emitter regions 12.

The mesa portion 61 of the diode portion 80 is not provided with theemitter region 12. An upper surface of the mesa portion 61 may beprovided with the base region 14 and the contact region 15. In a regionsandwiched between the base region 14-e in an upper surface of the mesaportion 61, the contact region 15 may be provided in contact with eachof the base regions 14-e. In a region sandwiched between the contactregions 15 in the upper surface of the mesa portion 61, the base region14 may be provided. The base region 14 may also be arranged in theentire region sandwiched between the contact regions 15.

In the transistor portion 70, a buffer region may be provided in aregion in contact with the diode portion 80. A mesa portion in thebuffer region is a dummy mesa portion having the same structure as themesa portion 61 of the diode portion 80. A lower surface of the dummymesa portion in the buffer region is provided with a collector region22. The buffer region is provided, so that it is possible to arrange acathode region 82 and the gate mesa portion apart from each other and tosuppress flow of carriers between the gate mesa portion and the cathoderegion 82.

The mesa portion in the buffer region may also have the contact region15 in the upper surface of the semiconductor substrate 10, instead of atleast a part of the base region 14 of the diode portion 80. In the mesaportion in the buffer region, an area of the contact region 15 in theupper surface thereof may be larger than an area of the contact region15 in an upper surface of one mesa portion 60. Thereby, it is possibleto easily extract carriers such as holes toward the emitter electrode 52upon turn-off of the transistor portion 70.

The contact hole 54 is provided above each of the mesa portions. Thecontact hole 54 is arranged in a region sandwiched between the baseregions 14-e. In the present example, the contact hole 54 is providedabove each of the contact region 15, the base region 14 and the emitterregion 12. The contact hole 54 is not provided in regions correspondingto the base region 14-e and the well region 11. The contact hole 54 mayalso be arranged at a center of the mesa portion 60 in the arrangementdirection (X-axis direction).

In the diode portion 80, a region adjacent to the lower surface of thesemiconductor substrate 10 is provided with the cathode region 82 of N+type. In the lower surface of the semiconductor substrate 10, a regionin which the cathode region 82 is not provided may be provided with thecollector region 22 of P+ type. In FIG. 6 , a boundary between thecathode region 82 and the collector region 22 is indicated by adashed-dotted line.

FIG. 7 shows an example of a cross-sectional view taken along a line b-bin FIG. 6 . The b-b cross-section is an XZ plane passing the emitterregion 12 and the cathode region 82. In the cross-section, thesemiconductor device 100 of the present example comprises asemiconductor substrate 10, an interlayer dielectric film 38, an emitterelectrode 52 and a collector electrode 24. The interlayer dielectricfilm 38 is provided on an upper surface of the semiconductor substrate10. The interlayer dielectric film 38 is a film including at least onelayer of a dielectric film such as silicate glass added with impuritiesof boron, phosphorous or the like, a thermally oxidized film and otherdielectric film. The interlayer dielectric film 38 is provided with thecontact holes 54 described in FIG. 6 .

The emitter electrode 52 is provided on the interlayer dielectric film38. The emitter electrode 52 is in contact with the upper surface 21 ofthe semiconductor substrate 10 through the contact holes 54 in theinterlayer dielectric film 38. The collector electrode 24 is provided onthe lower surface 23 of the semiconductor substrate 10. The emitterelectrode 52 and the collector electrode 24 are formed of a metalmaterial such as aluminum. As used herein, a direction (Z-axisdirection) in which the emitter electrode 52 and the collector electrode24 are connected to each other is referred to as ‘depth direction’.

The semiconductor substrate 10 has a drift region 18 of N− type. Thedrift region 18 is provided in each of the transistor portion 70 and thediode portion 80.

The mesa portion 60 of the transistor portion 70 is provided with theemitter region 12 of N+ type and the base region 14 of P− typesequentially from the upper surface 21-side of the semiconductorsubstrate 10. The drift region 18 is provided below the base region 14.The mesa portion 60 may also be provided with an accumulation region 16of N+ type. The accumulation region 16 is arranged between the baseregion 14 and the drift region 18.

The emitter region 12 is arranged between the upper surface 21 of thesemiconductor substrate 10 and the drift region 18. The emitter region12 is exposed on the upper surface 21 of the semiconductor substrate 10,and is provided in contact with the gate trench portion 40. The emitterregion 12 may also be in contact with the trench portions on both sidesof the mesa portion 60. The emitter region 12 has a doping concentrationhigher than the drift region 18.

The base region 14 is provided between the emitter region 12 and thedrift region 18. In the present example, the base region 14 is providedin contact with the emitter region 12. The base region 14 may also be incontact with the trench portions on both sides of the mesa portion 60.

The accumulation region 16 is provided below the base region 14. Theaccumulation region 16 has a doping concentration higher than the driftregion 18. The accumulation region 16 having a high concentration isprovided between the drift region 18 and the base region 14, so that itis possible to increase a carrier injection enhancement effect (IEeffect), thereby reducing an on-voltage. The accumulation region 16 mayalso be provided to cover an entire lower surface of the base region 14in each mesa portion 60.

In the mesa portion 61 of the diode portion 80, the base region 14 of P−type is provided in contact with the upper surface 21 of thesemiconductor substrate 10. The base region 14 of the diode portion 80functions as an anode region of the diode portion 80. The drift region18 is provided below the base region 14. In the mesa portion 61, theaccumulation region 16 may be provided below the base region 14.

In each of the transistor portion 70 and the diode portion 80, a bufferregion 20 of N+ type may be provided below the drift region 18. A dopingconcentration in the buffer region 20 is higher than a dopingconcentration in the drift region 18. The buffer region 20 may serve asa field stop layer configured to prevent a depletion layer, whichexpands from a lower end of the base region 14, from reaching thecollector region 22 of P+ type and the cathode region 82 of N+ type. Thebuffer region 20 may have a plurality of peaks or a single peak in adoping concentration distribution in the depth direction.

In the transistor portion 70, the collector region 22 of P+ type isprovided below the buffer region 20. In the diode portion 80, thecathode region 82 of N+ type is provided below the buffer region 20. Thecollector region 22 and the cathode region 82 are exposed on the lowersurface 23 of the semiconductor substrate 10 and are connected to thecollector electrode 24.

On the upper surface 21-side of the semiconductor substrate 10, one ormore gate trench portions 40 and one or more dummy trench portions 30are provided. Each trench portion ranges from the upper surface 21 ofthe semiconductor substrate 10 to the drift region 18 through the baseregion 14. In a region in which at least any one of the emitter region12, the contact region 15 and the accumulation region 16 is provided,each trench portion reaches the drift region 18 through the regions. Theconfiguration “the trench portion penetrates a doped region” is notlimited to a manufacturing sequence of forming the doped region and thenforming the trench portion. A manufacturing of forming trench portionsand then forming the doped region between the trench portions is alsoincluded in the configuration “the trench portion penetrates the dopedregion”.

As described above, the transistor portion 70 is provided with the gatetrench portion 40 and the dummy trench portion 30. The diode portion 80is provided with the dummy trench portion 30, and is not provided withthe gate trench portion 40.

In the present example, a boundary between the transistor portion 70 andthe diode portion 80 in the X-axis direction is a boundary between thecathode region 82 and the collector region 22. In the example of FIG. 7, the dummy trench portion 30 is arranged at an end of the transistorportion 70 in the X-axis direction.

The gate trench portion 40 has a gate trench, a gate insulating film 42and a gate conductive portion 44 provided in the upper surface 21 of thesemiconductor substrate 10. The gate insulating film 42 is providedcovering an inner wall of the gate trench. The gate insulating film 42may be formed by oxidizing or nitriding a semiconductor of the innerwall of the gate trench. The gate conductive portion 44 is provided on afurther inner side than the gate insulating film 42 inside the gatetrench. That is, the gate insulating film 42 insulates the gateconductive portion 44 and the semiconductor substrate 10 each other. Thegate conductive portion 44 is formed of a conductive material such aspolysilicon.

The gate conductive portion 44 may be provided longer than the baseregion 14 in the depth direction. In the cross-section, the gate trenchportion 40 is covered by the interlayer dielectric film 38 on the uppersurface 21 of the semiconductor substrate 10. The gate conductiveportion 44 is electrically connected to the gate wire. When apredetermined voltage is applied to the gate conductive portion 44, achannel by an inversion layer of electrons is formed on a surface layerof an interface of the base region 14 in contact with the gate trenchportion 40.

The semiconductor device 100 of the present example has a trench typegate structure. However, in another example, the semiconductor device100 may have a planar type gate structure. That is, the gate conductiveportion 44 may also be provided above the upper surface 21 of thesemiconductor substrate 10. The gate insulating film 42 may also beprovided between the gate conductive portion 44 and the upper surface 21of the semiconductor substrate 10.

In the cross-section, the dummy trench portion 30 may have the samestructure as the gate trench portion 40. The dummy trench portion 30 hasa dummy trench, a dummy insulating film 32 and a dummy conductiveportion 34 provided in the upper surface 21 of the semiconductorsubstrate 10. The dummy conductive portion 34 is electrically connectedto the emitter electrode 52. The dummy insulating film 32 is providedcovering an inner wall of the dummy trench. The dummy conductive portion34 is provided inside the dummy trench and provided on a further innerside than the dummy insulating film 32. The dummy insulating film 32insulates the dummy conductive portion 34 and the semiconductorsubstrate 10 each other. The dummy conductive portion 34 may be formedof the same material as the gate conductive portion 44. For example, thedummy conductive portion 34 is formed of a conductive material such aspolysilicon. The dummy conductive portion 34 may have the same length asthe gate conductive portion 44 in the depth direction.

In the present example, the gate trench portion 40 and the dummy trenchportion 30 are covered by the interlayer dielectric film 38 on the uppersurface 21 of the semiconductor substrate 10. Note that, bottoms of thedummy trench portion 30 and the gate trench portion 40 may each have adownwardly convex curved shape (a curve shape in a cross-section).

In the transistor portion 70, an oxygen concentration distribution inthe depth direction (K-K) of the semiconductor substrate 10 is similarto the oxygen concentration distribution shown in FIG. 2 or FIG. 3 . Inthe diode portion 80, an oxygen concentration distribution in the depthdirection (K-K) of the semiconductor substrate 10 is also similar to theoxygen concentration distribution shown in FIG. 2 or FIG. 3 . Thereby,it is possible to form the transistor portion 70 and the diode portion80 by using the semiconductor substrate 10 whose oxygen concentration isaccurately controlled. For this reason, it is possible to reducevariation in characteristics of the semiconductor device 100.

In the example of FIGS. 5 to 7 , the semiconductor device 100 comprisesboth the transistor portion 70 and the diode portion 80 on onesemiconductor substrate 10. In another example, the semiconductor device100 may comprise the transistor portion 70, and may not comprise thediode portion 80. In this case, a structure of the transistor portion 70is similar to the transistor portion 70 shown in FIGS. 6 and 7 . Thesemiconductor device 100 may also comprise the diode portion 80, and maynot comprise the transistor portion 70. In this case, a structure of thediode portion 80 is similar to the diode portion 80 shown in FIGS. 6 and7 .

FIG. 8 shows another example of the cross-sectional view taken along theline b-b in FIG. 6 . The semiconductor device 100 of the present examplecomprises an upper surface-side lifetime control region 92, in additionto the configuration of the semiconductor device 100 described in FIG. 7. The upper surface-side lifetime control region 92 is a region that isprovided on the upper surface 21-side of the semiconductor substrate 10and reduces a lifetime of carriers. The upper surface-side lifetimecontrol region 92 includes crystal defects such as VO defects. Thecarriers of the semiconductor substrate 10 recombine with the crystaldefects, so that the lifetime of carriers is reduced. In FIG. 8 ,density peak positions of the crystal defects in the depth direction aredenoted by x-marks. The upper surface-side lifetime control region 92 isa region including the density peak positions of the crystal defects.The crystal defects may be formed by irradiating impurities such ashelium ions, hydrogen ions or the like from the upper surface 21-side orthe lower surface 23-side of the semiconductor substrate 10. The densitypeak positions of the crystal defects correspond to concentration peakpositions of the impurities irradiated so as to form the crystaldefects.

The upper surface-side lifetime control region 92 is provided in thediode portion 80. The upper surface-side lifetime control region 92 maybe provided in the entire diode portion 80 in the X-axis direction. Thediode portion 80 is provided with the upper surface-side lifetimecontrol region 92, so that it is possible to reduce a reverse recoverytime in the diode portion 80, thereby reducing a reverse recovery loss.

The upper surface-side lifetime control region 92 may also be providedin the transistor portion 70. The upper surface-side lifetime controlregion 92 may also be provided continuously in the X-axis direction inthe diode portion 80 and in a part of the transistor portion 70 incontact with the diode portion 80. The upper surface-side lifetimecontrol region 92 is also provided in the part of the transistor portion70 in contact with the diode portion 80, so that it is possible tosuppress carriers from flowing from the upper surface-side of thetransistor portion 70 toward the cathode region 82.

FIG. 9 shows an example of the oxygen concentration distribution and acrystal defect density distribution in a J-J cross-section in FIG. 8 .The J-J cross-section is an YZ cross-section passing the uppersurface-side lifetime control region 92. Both a region in the diodeportion 80 where the upper surface-side lifetime control region 92 isprovided and a region in the transistor portion 70 where the uppersurface-side lifetime control region 92 is provided may have thedistributions shown in FIG. 9 .

The oxygen concentration distribution shown in FIG. 9 is similar to theoxygen concentration distribution shown in FIG. 2 or FIG. 3 . In FIG. 9, a vertical axis of the oxygen concentration distribution is an axisindicating each oxygen concentration by a percentage when the oxygenconcentration Omax at the concentration peak 144 is 100%. The oxygenconcentration distribution in FIG. 9 is an enlarged view of the vicinityof the concentration peak 144. In FIG. 9 , a vertical axis of thecrystal defect density distribution is a logarithmic axis, and ahorizontal axis is a linear axis indicating positions in the depthdirection.

The crystal defect density distribution in the depth direction of thesemiconductor substrate 10 has an upper surface-side density peak 154 ina region of the upper surface 21-side of the semiconductor substrate 10(i.e., a region raging from the center position Dc to the upper surface21 of the semiconductor substrate 10). The crystal defect densitydistribution has an upper surface-side slope 156 from the uppersurface-side density peak 154 toward the upper surface 21, and a lowersurface-side slope 155 from the upper surface-side density peak 154toward the lower surface 23. In the present example, the crystal defectsare formed by implanting ions such as helium from the upper surface21-side of the semiconductor substrate 10. In this case, since thecrystal defects are also formed in a region through which ions such ashelium have passed, a gradient of the upper surface-side slope 156 isgentler than a gradient of the lower surface-side slope 155. A depthposition of the upper surface-side density peak 154 substantiallycoincides with a peak position of a concentration distribution of ionssuch as helium irradiated so as to form the crystal defects. In anotherexample, the crystal defects may also be formed by implanting ions suchas helium from the lower surface 23-side of the semiconductor substrate10. In this case, the gradient of the lower surface-side slope 155 isgentler than the gradient of the upper surface-side slope 156.

In the oxygen concentration distribution, a depth range within which theoxygen concentration is equal to or greater than 50% of the oxygenconcentration Omax at the concentration peak 144 is denoted as R1, and adepth range within which the oxygen concentration is equal to or greaterthan 80% of the oxygen concentration Omax is denoted as R2. The uppersurface-side density peak 154 is preferably arranged within the depthrange R1.

The oxygen concentration within the depth range R1 has a smalldifference from the oxygen concentration Omax, and is accuratelycontrolled by the annealing temperature. For this reason, by setting arange of ions such as helium for forming the crystal defects in thedepth range R1, ions such as helium can be implanted into a region wherevariation in oxygen concentration is small. Since a density of crystaldefects to be formed varies depending on the oxygen concentration, it ispossible to reduce variation in density peak value Vmax at the uppersurface-side density peak 154.

The upper surface-side density peak 154 may also be arranged within thedepth range R2. Thereby, the variation in density peak value Vmax can befurther reduced.

Note that, the concentration peak 144 in the oxygen concentrationdistribution may also be arranged between the upper surface-side densitypeak 154 and the upper surface 21 of the semiconductor substrate 10.That is, the upper surface-side density peak 154 may be arranged at aposition overlapping the lower surface-side slope 145 in the oxygenconcentration distribution. Thereby, the upper surface-side density peak154 can be arranged in a region of the oxygen concentration distributionwhere the gradient is small. Therefore, even when the position of theupper surface-side density peak 154 in the depth direction varies, it ispossible to reduce the variation in oxygen concentration caused due tothe position variation and the variation in the density peak value Vmax.Also in this case, the upper surface-side density peak 154 is preferablyarranged within the range R1 or the range R2.

A length of the depth range R1 in the depth direction may also be equalto or greater than 10 μm. By setting the depth range R1 long, the uppersurface-side density peak 154 can be easily provided within the depthrange R1, and the variation in density peak value Vmax can be reduced. Alength of the depth range R2 in the depth direction may also be equal toor greater than 10 μm. Thereby, the variation in density peak value Vmaxcan be further reduced. The length of the depth range R1 or R2 may alsobe equal to or greater than 15 μm or equal to or greater than 20 μm.

The length of the depth range R1 or R2 can be controlled by theannealing conditions and the like. For example, when the annealing timeis set longer, oxygen can be distributed up to a deeper position in thesemiconductor substrate 10 at a concentration close to the solidsolubility limit. For this reason, the depth range R1 or R2 can belengthened. The annealing time may be 1 hour or longer, 5 hours orlonger or 10 hours or longer.

In addition, a distance L1 between the concentration peak 144 of theoxygen concentration distribution and the upper surface 21 of thesemiconductor substrate 10 may be equal to or greater than 5 μm andequal to or smaller than 20 μm. By setting the distance L1 small to someextent, it is possible to shorten a length of a region in which theoxygen concentration distribution changes relatively sharply. Thedistance L1 may also be equal to or shorter than 10 μm. The distance L1may also be smaller than a length of the dummy trench portion 30 in thedepth direction, which is shown in FIG. 5 and the like. On the otherhand, a distance between the upper surface-side density peak 154 and theupper surface 21 may be longer than the length of the dummy trenchportion 30 in the depth direction. Thereby, the upper surface-sidedensity peak 154 is arranged at a position overlapping the lowersurface-side slope 145 of the oxygen concentration distribution.

Note that, the semiconductor device 100 shown in FIG. 8 has the uppersurface-side lifetime control region 92 on the upper surface 21-side ofthe semiconductor substrate 10, and does not have a lifetime controlregion on the lower surface 23-side. That is, on the lower surface23-side of the semiconductor substrate 10, the crystal defect densitydistribution, the lifetime distribution and the like in the depthdirection do not have extreme values such as peaks, valleys and thelike.

On the lower surface 23-side of the semiconductor substrate 10, theinfluence of the initial oxygen concentration is stronger, as comparedto the upper surface 21-side, so that the variation in oxygenconcentration is likely to increase. The lifetime control region is notprovided on the lower surface 23-side, so that it is possible to reducethe variation in characteristics of the semiconductor device 100.

FIG. 10 shows a relation between the oxygen concentration and a forwardvoltage Vf when a semiconductor substrate having an oxygen concentrationdistribution that is substantially uniform in a depth direction isformed with the upper surface-side lifetime control region 92 as shownin FIG. 8 . As shown in FIG. 10 , the crystal defect density variesdepending on the oxygen concentration in the semiconductor substrate andthe forward voltage Vf also varies.

For this reason, when manufacturing a semiconductor device by using asemiconductor substrate having no oxygen concentration distribution asshown in FIGS. 1 to 9 , oxygen concentrations in prepared semiconductorsubstrates are measured in advance and the substrates are rankedaccording to the oxygen concentrations. Then, a semiconductor substrateof a rank corresponding to a use of the semiconductor device is used.Since the oxygen concentration in the semiconductor substratemanufactured by the MCZ method, the FZ method and the like is likely tovary, it is difficult to stably prepare a semiconductor substrate havinga predetermined oxygen concentration.

In contrast, like the examples shown in FIGS. 1 to 9 , when thesemiconductor substrate 10 is annealed, on condition that the solidsolubility limit is higher than the initial concentration of thesemiconductor substrate 10, it is possible to set the oxygenconcentration in the semiconductor substrate 10 to a predeterminedconcentration and to reduce the variation in oxygen concentration amongthe substrates. For this reason, it is possible to suppress variation inperformance of the semiconductor device 100 and to reduce thepreparation cost of the semiconductor substrate.

FIG. 11 compares characteristics of the semiconductor devices 100manufactured using two semiconductor substrates 10 having differentinitial concentrations of oxygen. The initial oxygen concentration ofthe semiconductor substrate 10 of Sample 1 is 4×10¹⁶/cm³, and theinitial oxygen concentration of the semiconductor substrate 10 of Sample2 is 4×10¹⁷/cm³. The structure of the semiconductor device 100 issimilar to the example of FIG. 8 . The semiconductor substrate 10 ofSample 1 is a substrate manufactured by the FZ method, and thesemiconductor substrate 10 of Sample 2 is a substrate manufactured bythe MCZ method.

The semiconductor substrates 10 were subjected to the annealing processat conditions that the solid solubility limit is 1.5 times as large as4×10¹⁷/cm³. The annealing conditions for Sample 1 and 2 are the same.For the manufactured semiconductor devices 100 of Sample 1 and 2, arelation between a collector-emitter voltage (Vce) and a collectorcurrent (Ic) was measured under atmospheres of 25° C. and 175° C. At anytemperature, the characteristics of Sample 1 and 2 were substantiallythe same.

As such, according to the semiconductor device 100 described in FIGS. 1to 9 , it is possible to reduce the variation in characteristics due tothe variation in initial oxygen concentration. Also, even when thesemiconductor substrates 10 manufactured by the different manufacturingmethods such as the MCZ method and the FZ method are used, it ispossible to manufacture the semiconductor devices 100 whosecharacteristics are substantially the same.

FIG. 12 shows another example of the semiconductor device 100. Thesemiconductor device 100 of the present example is different from thestructure of the semiconductor device 100 shown in FIG. 8 , in that alower surface-side lifetime control region 93 is provided. Theconfigurations except the lower surface-side lifetime control region 93are the same as the example shown in FIG. 8 .

The lower surface-side lifetime control region 93 is arranged on thelower surface 23-side of the semiconductor substrate 10 (i.e., in aregion from the center position Dc to the lower surface 23 of thesemiconductor substrate 10 in the depth direction). In the presentexample, the lower surface-side lifetime control region 93 may also beprovided at a position overlapping the buffer region 20. The lowersurface-side lifetime control region 93 may also be provided over arange wider than the upper surface-side lifetime control region 92 inthe X-axis direction. In the present example, the lower surface-sidelifetime control region 93 is provided in the diode portion 80 and thetransistor portion 70 in their entirety in the X-axis direction.

The structure and formation method of the lower surface-side lifetimecontrol region 93 are similar to the upper surface-side lifetime controlregion 92. However, the lower surface-side lifetime control region 93may also be formed by irradiating ions such as helium from the lowersurface 23-side of the semiconductor substrate 10.

The lower surface-side lifetime control region 93 is provided, so thatit is possible to control the carrier lifetime in the semiconductorsubstrate 10 with higher accuracy. Note that, the lower surface-sidelifetime control region 93 is preferably provided at a positionoverlapping the lower surface-side slope 145 of the oxygen concentrationdistribution. That is, the lower surface-side lifetime control region 93is not preferably provided in the flat region 147 shown in FIG. 3 .Thereby, it is possible to reduce the influence of the variation ininitial oxygen concentration. However, the lower surface-side lifetimecontrol region 93 may also be provided in the flat region 147.

While the embodiments of the present invention have been described, thetechnical scope of the invention is not limited to the above describedembodiments. It is apparent to persons skilled in the art that variousalterations and improvements can be added to the above-describedembodiments. It is also apparent from the scope of the claims that theembodiments added with such alterations or improvements can be includedin the technical scope of the invention.

EXPLANATION OF REFERENCES

10 . . . semiconductor substrate, 11 . . . well region, 12 . . . emitterregion, 14 . . . base region, 15 . . . contact region, 16 . . .accumulation region, 18 . . . drift region, 20 . . . buffer region, 21 .. . upper surface, 22 . . . collector region, 23 . . . lower surface, 24. . . collector electrode, 29 . . . linear portion, 30 . . . dummytrench portion, 31 . . . edge portion, 32 . . . dummy insulating film,34 . . . dummy conductive portion, 38 . . . interlayer dielectric film,39 . . . linear portion, 40 . . . gate trench portion, 41 . . . edgeportion, 42 . . . gate insulating film, 44 . . . gate conductiveportion, 52 . . . emitter electrode, 54 . . . contact hole, 60, 61 . . .mesa portion, 70 . . . transistor portion, 80 . . . diode portion, 81 .. . extension region, 82 . . . cathode region, 90 . . . edge terminationstructure portion, 92 . . . upper surface-side lifetime control region,93 . . . lower surface-side lifetime control region, 100 . . .semiconductor device, 102 . . . end side, 112 . . . gate pad, 120 . . .active portion, 130 . . . outer periphery gate wire, 131 . . .active-side gate wire, 141 . . . upper surface-side electrode, 142 . . .lower surface-side electrode, 143 . . . high oxygen concentration part,144 . . . concentration peak, 145 . . . lower surface-side slope, 146 .. . upper surface-side slope, 147 . . . flat region, 154 . . . uppersurface-side density peak, 155 . . . lower surface-side slope, 156 . . .upper surface-side slope

What is claimed is:
 1. A manufacturing method of a semiconductor devicecomprising a semiconductor substrate containing oxygen, themanufacturing method comprising: annealing an initial substrate so thata solid solubility limit concentration of oxygen with respect to theinitial substrate is to be higher than a current oxygen concentration inthe initial substrate; and thinning the initial substrate from a lowersurface-side of the initial substrate to form the semiconductorsubstrate.
 2. The manufacturing method according to claim 1, furthercomprising: preparing an MCZ substrate as the initial substrate.
 3. Themanufacturing method according to claim 1, further comprising: preparingan FZ substrate as the initial substrate.